Machines for measurement, checking and manufacturing purposes are known to comprise a rotary shaft which rotates the object to be operated upon. This object is locked to the shaft by a ring mounted on the shaft to provide an axial thrust for locking the object, for example by pressing a cone or a flange (or itself acting as a cone or flange) against respective counteracting member, so as to clamp the object between the elements and secure it rigidly to the shaft.
An example of a machine of this type is a balancing machine for vehicle wheels.
Known locking rings all comprise on the inner surface of their hole a screw thread by which they are engaged on the shaft, which is also threaded.
Some known locking rings are of the quick-mounting type, ie they comprise one or more sectors which engage the shaft via their threaded surface, and can be shifted radially outwards for disengagement from the shaft so that the locking ring can be rapidly slid axially along the shaft into position.
All known locking rings are based on securing the ring to the shaft by applying a helical torque and then producing the axial thrust for locking the object by applying a suitable clamping torque to the ring.
Known locking rings have the drawback of being necessarily provided with radial levers of a length which is greater the greater the torque to be obtained, in order to be able to apply the necessary clamping torque manually. However, as the shaft rotates at generally very high speed and as the levers project outwards beyond the ring, such levers represent a danger to operator safety.
A further drawback is that as the clamping torque is applied manually, it is not of constant value. Sometimes an excessive torque is applied, with resultant excessive stressing of the thread, and consequent considerable effort required to release the locking ring, with the risk that, for many types of quick-mounting rings, the locking action on the object may fail.